In association with satisfactory home medical care and community medical care in recent years, there is an increasing demand for analytical tools with which highly accurate in vitro diagnostic tests can be easily and quickly conducted by a user who does not necessarily have to be an expert in clinical testing. For example, dry-type in vitro diagnostic tools (e.g., biosensor) as typified by those for immunochromatographic tests do not require preparation of a reagent, and can very easily quantitatively or qualitatively analyze a suspected substance in a test solution.
The foregoing in vitro diagnostic tools typically comprise: a porous material in sheet form in which a test solution flows; a base sheet which holds the porous material; and a reagent carried in a part of the porous material. Moreover, due to a simple operation of supplying a fluid such as blood or urine containing a suspected substance to a predetermined contact portion of the porous material, the suspected substance can be easily and quickly analyzed.
Most porous materials used in conventional in vitro diagnostic tools have been single-layer membranes. On the other hand, development has also been conducted for a porous material in which microporous membranes are stacked. For example, Patent Literature 1 proposes a method in which two or more polymeric solutions are applied almost at once to a web-like support to form a double-layer liquid film, followed by washing, thereby to form a multi-layer microporous membrane.